5-HT is a neurotransmitter that mediates a diverse array of physiological responses by interacting with multiple 5-HT receptor subtypes. At least 14 5-HT receptor genes have been cloned and we have already identified variants in genes of several 5-HT receptor subtypes (5-HT1a, 5-HT2a, 5- HT2c, 5-HT5a, 5-HT6 and 5HT7). Relationship between the genotypes, behavior and biochemistry, is under investigation. However, the effect of variation in a single allele is obscure because of neuroadaptive processes and interaction with other genetic and environmental factors. Existence of variants resulting from alternative splicing or RNA editing might also complicate evaluation of the involvement of genotypes of 5-HT receptors in behavioral phenotypes. Therefore, it is important to demonstrate the functional variants in genes that control serotonergic signal transduction. Recently, Dr. Northup has established a method to reconstitute rat 5-HT2c 1G protein complexes in vitro. This system enables us to evaluate the functional properties of two common 5-HT2c receptor alleles (Cys23 and Ser23) including their interaction with G protein subunits (paper is now in preparation). Additional baculoviral vectors have been prepared to explore, in this reconstituted system, the functional properties of three variants of 5-HT1a and three variants of 5-HT2a receptors to reconstitute these receptors.